Status Updates From Introduction to Forensic An...

“The general method of estimating PMI using these older methods was to categorize the amount of decomposition seen in a case into one of the decompositional stages. Then PMI is estimated as the observed range for that stage. However, if additional factors are known this estimate can be refined.”

“For example, if a body discovered during the summer fit the criteria for a stage with a range of 1 to 6 months, the PMI estimate might be drawn from the lower end of the range, because decomposition is accelerated during this time of year. Conversely, if the same remains were found in winter, an estimate of PMI might be drawn from the high end of the range.”

“Although no standards exist, the best approach was to draw from either end of the time range, depending on the nature of these factors.“

“Finally, descriptions of changes are drawn from all times of the year, thereby muddling the effects of temperature fluctuations. Considering these factors, and that these older methods are usually not associated with any statistical basis to communicate confidence intervals, it is important that current practitioners use most up to date methods discussed in the Accumulated Degree days section.”

“Third, because the process is continuous, individual bodies sometimes fit the characteristics of two (and even three) of these stages, causing some confusion as to the best estimate of PMI. Fourth, most schedules of decomposition are derived from exposed (e.g., surface) finds; this makes estimating PMI for burials and remains found in water difficult.”

“…climatic factors affect the rate of soft tissue loss. Thus, a single schedule of decomposition for all geographic areas is not possible to attain…Second, all studies find a large range of variation in the time needed to reach these stages various stages of decomposition. This variation causes overlaps of time ranges between categories of deterioration, with concomitant uncertainty in PMI estimates.”

“The decomposition process starts with a fresh human body and proceeds through a series of changes until (given enough time) full skeleton I action is achieved. A common device used to simplify this complex process is to divide it into identifiable stages. PMI can then be estimated by knowing the time needed by the body to reach these stages of deterioration.”

“The broad area of entomology (the study of insects) includes forensic entomology, which is the study of insect life cycle and succession on cadavers for the purpose of estimating PMI. Similarly, forensic scientists within botany (forensic botany) use plant growth as a method of estimating this interval.”

Chapter 5 Estimating PMI (postmortem interval)